Fuel cells have been proposed as a clean, efficient, and environmentally responsible power source for electric vehicles and various other applications. In particular, fuel cells have been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically positioned between porous diffusion media (DM), such as carbon fiber paper, which facilitate delivery of reactants such as hydrogen to the anode and oxygen, typically from air, to the cathode. In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
The electrolyte membrane is typically formed from a layer of ionomer. A typical ionomer is a perfluorosulfonic acid (PFSA) polymer, such as Nafion®, commercially available from the E.I. du Pont de Nemours and Company. The electrodes of the fuel cell are generally formed from a finely divided catalyst. The catalyst may be any electro-catalyst that catalytically supports at least one of an oxidation of hydrogen and a reduction of oxygen for the fuel cell electrochemical reaction. The catalyst may be a precious metal such as platinum or another platinum-group metal. The catalyst is generally disposed on a carbon support, such as carbon black particles, and is dispersed in an ionomer. The electrolyte membrane, electrodes, and DM are positioned between a pair of fuel cell plates and sealed, for example, with a gasket providing a substantially fluid-tight seal.
The electrolyte membrane also typically has a barrier film or subgasket coupled thereto to provide internal reinforcement and to separate the hydrogen gas and the air supplied to the fuel cell stack. The subgasket generally overlays an edge of the electrolyte membrane and is formed in a secondary operation by cutting a piece of polymeric sheet material and bonding the sheet material to the electrolyte membrane with at least one of compression and an adhesive. Some examples of subgaskets and means for coupling subgaskets to the electrolyte membrane are described in commonly-owned U.S. Pat. No. 7,935,453, the entirety of which is hereby incorporated herein by reference.
A subgasket that follows a periphery of the fuel cell plate active area abuts the MEA and can overlap the MEA. The subgasket generally functions both to support the MEA and to electrically insulate the cathode flow field of a fuel cell from the anode flow field of an adjacent fuel cell in a stacked assembly. The subgasket also electrically insulates the regions outside the flowfield. An inner edge of the subgasket defines the active region of the MEA.
Rigorous conditions such as high temperature and high pressure, both of which are encountered during normal operation of fuel cells, necessitate constructing the various components of the fuel cell from materials that do not degrade or deform. Common causes of degradation or deformation include localized areas of high compression when thick subgaskets are used or areas of subgasket deflection by the flow of reactant gases when thin subgaskets are used. Such degradations or deformations of the subgasket may negatively affect the life of the MEA or may decrease the performance of the fuel cell as a whole.
There remain ongoing needs, therefore, for improved subgaskets that can be incorporated into MEAs, fuel-cell assemblies including the MEAs, and fuel-cell stacks including one or more of the fuel-cell assemblies, with which the problems of subgasket degradation and deformation can be addressed without sacrificing manufacturing costs or production output.